Luteinizing hormone receptor concentrations, adenylate cyclase activity and phosphodiesterase activity of bovine corpora lutea: Comparison of short and normal estrous cycles

Abstract

Concentrations of unoccupied and occupied luteinizing hormone (LH) receptors, basal and agonist-activated adenylate cyclase activities and phosphodiesterase activity of corpora lutea from seventeen postpartum beef cows anticipated to have a short or normal luteal lifespan were compared. Calves were weaned 26 to 33 days postpartum and the cows assigned to groups 1 or 2. In group 1 (n=8), corpora lutea were removed on day 5 (day 0 = estrus) following the first and third estrus. In group 2 (n=9), lutectomy occurred on day 5 following the third estrus. The length of the first estrous cycle ranged from 7 to 12 days, ( x ± SD =8.1 ± 1.6 days ) in eight of nine cows in group 2 and the mean ( x ± SE ) length of the second estrous cycle for groups 1 and 2 was 19.6 ± .2 and 20.9 ± .4 days, respectively. Luteal weight, luteal progesterone concentration, plasma progesterone concentration, luteal unoccupied and occupied LH receptor concentrations, and luteal adenylate cyclase (basal and agonist-activated) activities were similar (P>.05) on day 5 of the first (group 1) and third (groups 1 and 2) estrous cycles. The preceding plasma and luteal measurements were similar (P>.05) on day 5 of the third estrous cycle for groups 1 and 2. Luteal phosphodiesterase activity was similar (P>.05) for groups 1 and 2 on day 5 of the third estrous cycle, but higher (P<.05) on day 5 of the first compared to the third estrous cycle (groups 1 and 2). In summary, subnormal luteal function does not appear to be due to a decrease in unoccupied LH receptors, occupied LH receptors, or adenylate cyclase activity. It is unlikely that an increase in phosphodiesterase activity decreases luteal lifespan, since the increase in enzyme activity was not accompanied by a decrease in concentration of luteal or plasma progesterone.